Abstract
The molar enthalpies of mixing, Δ mix H m in the binary liquid systems TbBr 3 -MBr (M = Li, Na, K, Rb, Cs) have been m easured with a Calvet-type high-tem perature microcalorimeter over the entire composition range with an accuracy of about 6 %. Mixing of the two liquid components was achieved by using the “break-off am poule” technique. All the investigated systems show negative enthalpies of mixing with a minim um value of approxim ately -1.25, - 8 .3 , -17.0, - 2 0 . 0 and -22.5 kJ mol -1 , for M = Li, Na, K, Rb and Cs, respectively. The mixing enthalpy in the TbBr 3 - LiBr system is positive in the TbBr 3 -rich region. For all the systems, the enthalpy minimum occurs at mole fraction x TbBr3 ≈ 0.3 - 0.4. The molar enthalpies of form ation Δ form H m (3MBr, TbBr 3 , 1) for M = Li, Na, K, Rb and Cs at 1113 K (arising from the reaction 3M Br (1) +TbBr3 (1) = (3MBr, TbBr 3 ) (1) ) are found to be -4 .8 , -31.3, -63.3, -70.3 and -8 1 .2 kJ mol -1 , respectively. The leastsquares coefficients A, B, C, D and E in the equation λ (kJ mol -1 ) = A + B x + C x 2 + Dx 3 + Ex 4 , where A is an interaction param eter and x = x TbBr , are also reported.